Cocaine abuse continues to be a significant public health concern. Relapse rates to cocaine use after treatment remain discouragingly high even with the advent of sophisticated behavioral and cognitive relapse prevention therapies. Identifying an effective pharmacological adjunct will likely be necessary to further reduce cocaine relapse rates. The specific aim of this proposal is to demonstrate that aripiprazole is an effective "anti-relapse" medication for cocaine, and possibly determine the behavioral mechanism by which it exerts this effect (i.e., aripiprazole attenuates the discriminative effects of priming doses of cocaine thereby reducing subsequent drug self-administration). To accomplish this aim, we will first determine the safety and tolerability of cocaine-aripiprazole combinations by administering ascending doses of oral and intranasal cocaine doses during aripiprazole maintenance, and monitoring physiological and behavioral responses (Exp. 1). We will then demonstrate that chronic aripiprazole treatment attenuates the discriminative-stimulus effects of cocaine (Exp. 2). The discriminative-stimulus effects of drugs may be involved in relapse to drug taking behavior in that the initial or priming dose (i.e., a lapse) functions as a discriminative stimulus that signals the availability of more cocaine. Finally, Exp. 3 will demonstrate that a priming dose of cocaine (i.e., a lapse) increases subsequent cocaine taking using a novel self-administration procedure designed to model relapse, and that aripiprazole attenuates this effect. Aripiprazole was chosen for study because it is a potent partial agonist at the dopamine (DA) D2 and serotonin (5-HT) 5-HT1A receptors. Cocaine is thought to exert its effects by blocking monoamine transporters (e.g., DA and 5-HT). Partial agonists may represent a novel and effective means to prevent relapse to cocaine use because theoretically they should have the therapeutic advantages of both an agonist and an antagonist. Consistent with this notion, the results of a recent experiment conducted in our laboratory suggest that acutely administered aripiprazole significantly attenuates the discriminative-stimulus and subjective effects of d-amphetamine in humans. We are unaware of any published reports in which the effects of cocaine were assessed in humans following pretreatment with aripiprazole. The proposed research will provide the initial clinical information regarding the efficacy of aripiprazole as a putative "anti-relapse" medication for cocaine dependence. The conduct of the proposed controlled laboratory studies will provide important information (e.g., appropriate doses) that will guide the design of a subsequent clinical trial. Reducing relapse to drug use is important because intravenous abuse of cocaine may be associated with increased risk of acquired immunodeficiency syndrome (A.I.D.S.).